Iodide [(η5-indenyl)IrI2]n: an effective precursor to (indenyl)iridium sandwich complexes

Article abstract of DOI:10.1016/j.mencom.2016.11.010

The reactions of [(η⁵-indenyl)IrI₂]_η with CpTl or arenes in the presence of AgBF₄ afford [(η⁵-indenyl)IrCp]⁺ or [(η⁵-indenyl)Ir(arene)]²⁺ cations (arene = benzene, mes

Full text of DOI:10.1016/j.mencom.2016.11.010

Mendeleev
Communications
Mendeleev Commun., 2016, 26, 491–493
Iodide [(h5-indenyl)IrI2]n: an effective precursor
to (indenyl)iridium sandwich complexes
Alexander A. Chamkin, Anastasiia M. Finogenova, Yulia V. Nelyubina,
Julia Laskova, Alexander R. Kudinov* and Dmitry A. Loginov*
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119991 Moscow,
Russian Federation. Fax: +7 499 135 5085; e-mail: arkudinov@ineos.ac.ru, dloginov@ineos.ac.ru
DOI: 10.1016/j.mencom.2016.11.010
The reactions of [(h5-indenyl)IrI2]n with CpTl or arenes
in the presence of AgBF4 afford [(h5-indenyl)IrCp]+ or
[(h5-indenyl)Ir(arene)]2+ cations (arene = benzene, mesitylene,
durene or hexamethylbenzene); the structures of (h5-indenyl)-
Ir(C2H4)2 and [(h5-indenyl)IrCp]PF6 were characterized by
X-ray diffraction analysis.
+
2+
Ir
Ir
I2
Ir
Rn
n
In the last decade, the halide cyclopentadienyl rhodium and
iridium complexes [(C5R5)MX2]2 proved to be effective catalysts
for the C–H activation of aromatic compounds.1 Moreover, they
are widely used as the synthons of (C5R5)M fragments in organo-
metallic synthesis.2 For example, we prepared a number of arene,
triple-decker and metallacarborane complexes using the reac-
tions of [(C5R5)M]2+ cationic species (generated by a reaction
of [(C5R5)MX2]2 with silver salts) with arenes, sandwich com-
pounds and carborane ligands.3 The related indenyl complexes
spectrum of 1, there are only signals from the indenyl system.
The polymeric structure was suggested based on the insolubility
of 1 in dichloromethane, acetone and acetonitrile and on an analog
y
with the cyclopentadienyl derivative [CpIrI2]n. Recently, we have
shown that the cyclooctadiene complex CpIr(cod) reacts with
halogens giving cationic complexes [CpIr(cod)X]X containing a
coordinated cyclooctadiene ligand.6 However, a similar reaction
of (h5-indenyl)Ir(cod) with I2 leads to an unidentified mixture
of products, the formation of which is probably caused by the
partial elimination of cyclooctadiene.
attract considerable attention due to their higher chemical reactivit
y
(indenyl effect). The enhanced reactivity is caused by the easy
slippage of an indenyl ligand from h5 to h3 coordination mode.
Here, we report the synthesis of the iodide [(h5-indenyl)IrI2]n
and demonstrate its applicability to the preparation of sandwich
compounds containing the (h5-indenyl)Ir moiety.
i, ethylene
ii, [indenyl]Li
I2
Ir
Ir
I2
Ir
Cl
n
The iodide [(h5-indenyl)IrI2]n 1† was synthesized by the Bergman
method4 based on a reaction of iodine with the bis(ethylene)
derivative (h5-indenyl)Ir(C2H4)2 (Scheme 1). The latter was
prepared without purification from the cyclooctene complex
[(C8H14)2IrCl]2,5,‡ ethylene and indenyllithium.§ In the 1H NMR
2
1
Scheme 1
Iodide 1 proved to be an effective synthon of the (h5-indenyl)Ir
species. For example, the reaction of 1 with CpTl affords the mixed
ligand sandwich cation [(h5-indenyl)IrCp]+ 2¶ (Scheme 2).††
†
Ethylene was passed through a solution of [(C8H14)2IrCl]2 (700 mg,
0.78 mmol) in THF (10 ml) for 20 min. A solution of indenyllithium
(0.25 m, 7.6 ml, 1.9 mmol) was added to the dark red reaction mixture
with stirring under argon. The resulting greenish solution was kept with
stirring for two days. The solvent was removed in vacuo and the residue
was chromatographed on SiO2 (20 cm × 1 cm) by elution with light
petroleum and then diethyl ether. The light yellow band was collected and
evaporated in vacuo to give [(h5-indenyl)Ir(C2H4)2] as a pale brown oily
solid. A solution of I2 (400 mg, 1.57 mmol) in Et2O (8 ml) was added to
[(h5-indenyl)Ir(C2H4)2] in the same solvent (4 ml) in air, and the reaction
mixture was stirred for 1 h. The dark brown precipitate was centrifuged
off, washed three times with Et2O, one time with CH2Cl2 and then was
washed with Et2O until discoloration of the solvent. The residue was dried
in vacuo. Yield, 400 mg (46%) as a dark purple presumably polymeric
substance. 1H NMR (DMSO-d6) d: 7.56–7.60 (m, 4H, indenyl), 6.52 (m,
2H, indenyl), 6.27 (m, 1H, indenyl). Found (%): C, 19.34; H, 1.31. Calc.
for C9H7I2Ir (%): C, 19.26; H, 1.26.
argon. The reaction mixture was refluxed with vigorous stirring for 4 h.
The upper water-alcohol layer was decanted and cold EtOH (7 ml) was
added to the orange oily residue. The resulting mixture was kept at 0°C
for ~16 h. The precipitate formed was filtered off, washed with cold EtOH
and dried in vacuo. Yield, 1.31 g (65%) as an orange solid.
§
A solution of BuLi (2.5 m, 2.8 ml, 7 mmol) in hexanes was added to
a solution of indene (1 g, 8.6 mmol) in THF (25 ml) with stirring under
argon. The mixture was stirred for ~1 h. The solution obtained (2.5 m of
indenyllithium in hexanes–THF) was used without further isolation.
¶
Dry MeCN (2 ml) was added to a mixture of 1 (60 mg, 0.107 mmol)
and CpTl (38 mg, 0.14 mmol) under argon. The solution was stirred for
3 h and then filtered; the solvent was removed in vacuo. The residue was
treated with a saturated aqueous solution of KPF6. The aqueous layer was
decanted and the solid residue was twice washed with water. After drying
over P2O5, product [2]PF6 was obtained as a white solid, yield 35 mg
(63%). 1H NMR (acetone-d6) d: 7.66 (m, 2H, indenyl), 7.39 (m, 2H,
indenyl), 6.7 (d, 2H, indenyl, J 2.8 Hz), 6.0 (t, 1H, indenyl, J 2.8 Hz),
5.83 (s, 5H, Cp). Found (%): C, 32.37; H, 2.29. Calc. for C14H12F6IrP (%):
C, 32.50; H, 2.34.
‡
The cyclooctene complex [(C8H14)2IrCl]2 was prepared by a well-known
procedure5 with the use of K2IrCl6 instead of (NH4)3IrCl6. A degassed
mixture of H2O (30 ml) and PriOH (10 ml) was stirred while cis-cyclo-
octene (4 ml, 31 mmol) and K2IrCl6 (2.2 g, 4.54 mmol) were added under
© 2016 Mendeleev Communications. Published by ELSEVIER B.V.
on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.
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Mendeleev Commun., 2016, 26, 491–493
+
C(6)
C(7)
C(8)
C(5)
C(4)
C(2)
CpTl
Ir
I2
Ir
C(1)
C(3)
C(9)
n
Ir(1)
1
2
C(13)
C(12)
Scheme 2
C(10)
C(11)
We found that iodide abstraction from 1 by AgBF4 in nitro-
methane in the presence of benzene and its derivatives resulted
in dicationic arene complexes [(h5-indenyl)Ir(arene)]2+ 3a–d
(Scheme 3).‡‡ Note that the intermediate solvates [(h5-indenyl)-
Ir(MeNO2)3]2+ are unstable in nitromethane solution. Thus, a
control experiment with their preliminary generation and sub-
sequent interaction with benzene did not give target complex 3a.
The thermal instability of the solvate complexes did not allow us
to prepare polymethylated complexes 3c,d in analytically pure
forms owing to their low formation rates.
Figure 1 One of the two independent molecules of the complex (h5-indenyl)-
Ir(C2H4)2 with atoms shown as thermal ellipsoids at a 50% probability level.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å): Ir(1)–C(1)
2.355(5), Ir(1)–C(2) 2.199(5), Ir(1)–C(3) 2.210(5), Ir(1)–C(4) 2.212(6),
Ir(1)–C(5) 2.374(5), Ir(1)–C(10) 2.131(6), Ir(1)–C(11) 2.108(6), Ir(1)–C(12)
2.130(6), Ir(1)–C(13) 2.132(6), C(1)–C(2) 1.450(8), C(2)–C(3) 1.431(8),
C(3)–C(4) 1.424(8), C(4)–C(5) 1.448(7), C(1)–C(5) 1.438(7), C(10)–C(11)
1.423(9), C(12)–C(13) 1.439(8).
C(6)
C(7)
C(8)
C(5)
C(4)
C(2)
C(3)
C(1)
C(9)
2+
Ag+, C6H6 – nRn
Ir(1)
Ir
I2
Ir
– AgI
Rn
3c Rn = 1,2,4,5-Me4
n
C(14)
C(10)
C(13)
C(11)
C(12)
1
3a Rn = H
3b Rn = 1,3,5-Me3 3d Rn = Me6
Figure 2 Cation 2 with atoms shown as thermal ellipsoids at a 50% probability
level. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å):
Ir(1)–C(1) 2.254(13), Ir(1)–C(2) 2.162(14), Ir(1)–C(3) 2.178(15), Ir(1)–C(4)
2.168(15), Ir(1)–C(5) 2.223(12), Ir(1)–C(10) 2.161(15), Ir(1)–C(11) 2.174(14),
Ir(1)–C(12) 2.157(15), Ir(1)–C(13) 2.181(14), Ir(1)–C(14) 2.172(14),
C(1)−C(2) 1.445(19), C(2)–C(3) 1.39(3), C(3)–C(4) 1.42(3), C(4)–C(5)
1.46(3), C(1)–C(5) 1.448(19), C(10)–C(11) 1.43(2), C(11)–C(12) 1.41(3),
C(12)–C(13) 1.42(2), C(13)–C(14) 1.37(2), C(10)–C(14) 1.41(2).
Scheme 3
The salts [2]PF6 and [3a–d](BF4)2 are air-stable solids. More-
over, the benzene derivative [3a](BF4)2 is stable in dry acetonitrile
solution for at least two days, similar to [CpIr(C6H6)](BF4)2.3(b)
In the 1H NMR spectrum of [3a](BF4)2, the signal of the protons
of a coordinated benzene ligand is very close (Dd = 0.04 ppm)
to that for free benzene. This is a consequence of a high positive
charge, whose effect compensates the opposite effect of coor-
atom with moderate slippage; the hinge angles†††,8 are 7.7–8.0°
and 7.3°, respectively. The slip parameter‡‡‡ is another charac-
teristic used to describe the slip–fold distortion in the indenyl
complexes.1 Note that this parameter considerably increased on
going from cation 2 (0.074 Å) to a bis(ethylene) derivative
(0.163 Å). This is in accordance with a general tendency to the
more favorable formation of 16VE complexes for Iri than for Iriii.
For other Iri complexes, (h5-indenyl)Ir(cod)9 and (h5-indenyl)-
Ir(h4-HC4Tol4Ph),10 the slip parameter also achieves high values
(0.149 and 0.155 Å, respectively).
dination to the transition metal atom.
§§,7
The structures of (h5-indenyl)Ir(C2H4)2
and [2]PF6 were
determined by X-ray diffraction analysis (Figures 1 and 2).¶¶ The
indenyl ligand in both complexes is h5-coordinated to the iridium
†† Anions are omitted in the schemes for clarity.
‡‡ Dry MeNO2 (1 ml) was added to a mixture of 1 (60 mg, 0.107 mmol),
AgBF4∙C4H8O2 (61 mg, 0.214 mmol) and arene (0.5 ml of benzene or
mesitylene; 60 mg, 0.43 mmol of durene; 70 mg, 0.43 mmol of hexa-
methylbenzene) with stirring under argon. The reaction mixture was kept
for 1 h with stirring; then, the solvent was removed in vacuo and the oily
residue was dissolved in MeNO2 (0.5 ml). After the solution was filtered,
the product was reprecipitated from MeNO2 by diethyl ether, centrifuged
off and washed with diethyl ether three times.
The C–C bond lengths of coordinated ethylene in (h5-indenyl)-
Ir(C2H4)2 [1.423(9)–1.439(8) Å, av. 1.43 Å] are close to those in
cyclopentadienyl analogues (h-C5H4R)Ir(C2H4)2 (1.40–1.44 Å)11
¶¶ Crystals of (h5-indenyl)Ir(C2H4)2 were grown by the slow evaporation
of light petroleum solution. Crystals of [2]PF6 were grown up by slow
diffusion in two-layer system, diethyl ether and a solution of the complex
in acetone.
Crystal data for (h5-indenyl)Ir(C2H4)2: C13H15Ir, monoclinic, space
group P21/c, a = 7.7314(3), b = 10.7823(4) and c = 25.7026(10) Å,
b = 98.4434(8)°, V = 2119.40(14) Å3, Z = 8, dcalc = 2.278 g cm–3, m =
= 12.554 mm–1, F(000) = 1360, R1 = 0.0352 [from 5586 unique reflec-
tions with I > 2s(I)] and wR2 = 0.0888 (from all 6184 unique reflections).
Crystal data for [2]PF6: C14H12F6IrP, monoclinic, space group P21/n,
a = 9.0455(11), b = 13.9932(17) and c = 11.2372(13) Å, b = 92.647(2)°,
V = 1420.8(3) Å3, Z = 4, dcalc = 2.419 g cm–3, m = 9.568 mm–1, F(000) =
= 968, R1 = 0.0648 [from 3478 unique reflections with I > 2s(I)] and
wR2 = 0.1841 (from all 4149 unique reflections).
For [3a](BF4)2: yield 24 mg (40%) as a golden brown solid. 1H NMR
(CD3NO2) d: 7.92 (m, 2H, indenyl), 7.85 (m, 2H, indenyl), 7.41 (s, 6H,
C6H6), 7.36 (d, 2H, indenyl, J 2.5 Hz), 6.7 (t, 1H, indenyl, J 2.5 Hz).
Found (%): C, 32.04; H, 2.33. Calc. for C15H13B2F8Ir (%): C, 32.22;
H, 2.34.
For [3b](BF4)2: yield 47 mg (73%) as an orange solid. 1H NMR
(CD3NO2) d: 8.00 (m, 2H, indenyl), 7.78 (m, 2H, indenyl), 7.16 (d, 2H,
indenyl, J 2.9 Hz), 7.12 (s, 3H, C6H3Me3), 6.66 (t, 1H, indenyl, J 2.9 Hz),
2.57 (s, 9H, C6H3Me3). Found (%): C, 35.97; H, 3.15. Calc. for C18H19B2F8Ir
(%): C, 35.96; H, 3.19.
For [3c](BF4)2: yield 14 mg (22%) as a cream solid. 1H NMR (CD3NO2)
d: 8.07 (m, 2H, indenyl), 7.65 (m, 2H, indenyl), 7.30 (s, 2H, C6H2Me4),
7.15 (d, 2H, indenyl, J 2.5 Hz), 6.49 (t, 1H, indenyl, J 2.5 Hz), 2.35 (s,
12H, C6H2Me4).
For [3d](BF4)2: yield 4 mg (6%) as a cream solid. 1H NMR (CD3NO2)
d: 8.09 (m, 2H, indenyl), 7.65 (m, 2H, indenyl), 6.91 (d, 2H, indenyl,
J 2.5 Hz), 6.47 (t, 1H, indenyl, J 2.5 Hz), 2.46 (s, 18H, C6Me6).
§§ The structure of (h5-indenyl)Ir(C2H4)2 was studied earlier by Merola.7
In this study, a crystal had the same crystallographic parameters. The
crystallographic cell contains two independent molecules; data for only
one of them will be used in the discussion.
CCDC 1477235 and 1477236 contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk.
†††
The hinge angle is defined as an angle between the planes defined by
C(2)C(3)C(4) and C(2)C(1)C(5)C(4).
‡‡‡
The slip parameter is defined as difference between the average
distances from the metal to bridgehead carbons and from the metal to
adjacent carbon atoms.
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Mendeleev Commun., 2016, 26, 491–493
and longer than that in free ethylene (1.333 Å).12 The Ir∙∙∙C9H7
and P. M. Maitlis, J. Organomet. Chem., 1984, 272, 265; (d) X. L. R.
Fontaine, N. N. Greenwood, J. D. Kennedy, K. Nestor, M. Thornton-
Pett, S. Herˇmánek, T. Jelinek and B. Štibr, J. Chem. Soc., Dalton Trans.,
1990, 681; (e) G. E. Herberich, U. Englert, F. Marken and P. Hofmann,
Organometallics, 1993, 12, 4039.
distance in 2 (1.828 Å) is longer than the Ir∙∙∙C5Me5 distances
+
in iridocenium cations [CpIrCp*]+ (av. 1.798 Å)13 and [IrCp2 ]
*
(av. 1.819 Å),14 suggesting the weaker bonding of iridium with
an indenyl ligand than with Cp.
3 (a) A. R. Kudinov, D. A. Loginov, Z. A. Starikova and P. V. Petrovskii,
J. Organomet.Chem.,2002,649,136;(b)D.A.Loginov,M.M.Vinogradov,
Z. A. Starikova, P. V. Petrovskii and A. R. Kudinov, Russ. Chem. Bull.,
Int. Ed., 2004, 53, 1949 (Izv. Akad. Nauk, Ser. Khim., 2004, 1871);
(c) D. A. Loginov, D. V. Muratov, P. V. Petrovskii, Z. A. Starikova,
M. Corsini, F. Laschi, F. de Biani Fabrizi, P. Zanello and A. R. Kudinov,
Eur. J. Inorg. Chem., 2005, 1737; (d) D. A. Loginov, D. V. Muratov,
Z. A. Starikova, P. V. Petrovskii and A. R. Kudinov, Russ. Chem. Bull.,
Int. Ed., 2006, 55, 1581 (Izv. Akad. Nauk, Ser. Khim., 2006, 1525);
(e) D. A. Loginov, D. V. Muratov, Z. A. Starikova, P. V. Petrovskii and
A. R. Kudinov, J. Organomet. Chem., 2006, 691, 3646; (f) D. A. Loginov,
Z.A. Starikova, M. Corsini, P. Zanello andA. R. Kudinov, J. Organomet.
Chem., 2013, 747, 69.
Recently, we have found that the cyclopentadienyl complexes
[CpMI2]2 (M = Rh, Ir) effectively catalyze the oxidative coupling of
benzoic acid with diphenylacetylene to give 1,2,3,4-tetraphenyl-
naphthalene.15 Taking into account that indenyl complexes often
exhibit higher catalytic activity as compared to that of cyclopenta-
dienyl analogues,16 we tried to use complex 1 as a catalyst in this
reaction. Unfortunately, this complex was found catalytically
inactive. For example, the reaction in the presence of 2 mol% of
the catalyst afforded 1,2,3,4-tetraphenylnaphthalene in only 12%
yield.§§§ At the same time, the use of an equimolar quantity of 1
increased the yield up to 98%. This behaviour can be explained
by the low stability of the (h5-indenyl)Ir species, which were
proposed as catalytic intermediates, under reaction conditions
(refluxing in o-xylene).
4 T. Foo and R. G. Bergman, Organometallics, 1992, 11, 1801.
5 A. van der Ent and A. L. Onderdelinden, Inorg. Synth., 1973, 14, 92.
6 D. A. Loginov, A. M. Miloserdov, Z. A. Starikova, P. V. Petrovskii and
A. R. Kudinov, Mendeleev Commun., 2012, 22, 192.
7 J. S. Merola, Acta Crystallogr., 2013, E69, m547.
In summary, we have demonstrated that iodide 1 can be used
as a synthon of the (indenyl)iridium fragment (h5-indenyl)Ir for
the preparation of its cyclopentadienyl and arene derivatives.
8 (a) J. W. Faller, R. H. Crabtree and A. Habib, Organometallics, 1985,
4, 929; (b) S. A. Westcott, A. K. Kakkar, G. Stringer, N. J. Taylor and
T. B. Marder, J. Organomet. Chem., 1990, 394, 777.
9 P. Cecchetto, A. Ceccon, A. Gambaro, S. Santi, P. Ganis, R. Gobetto,
G. Valle and A. Venzo, Organometallics, 1998, 17, 752.
This work was supported by the Russian Science Foundation
(project no. 16-33-60140 mol_a_dk).
10 M. C. Comstock and J. R. Shapley, Organometallics, 1997, 16, 4816.
11 (a) G. Kohl, R. Rudolph, H. Pritzkow and M. Enders, Organometallics,
2005, 24, 4774; (b) F. Bertini, L. Calucci, F. Cicogna, B. Gaddi, G. Ingrosso,
M. Marcaccio, F. Marchetti, D. Paolucci, F. Paolucci and C. Pinzino,
J. Organomet. Chem., 2006, 691, 2987; (c) R. M. Chin, D. Maurer, M. Parr,
N. Allworth, R. Schwenker, D. Sullivan, S. Enabnit and W. Brennessel,
Inorg. Chim. Acta, 2009, 362, 389.
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§§§
A mixture of benzoic acid, diphenylacetylene, Ag2CO3, 1 and o-xylene
was refluxed with stirring under argon for about 6 h. The solvent was
removed in vacuo and the residue was chromatographated on SiO2
(15 cm × 1 cm) by elution with light petroleum first and then diethyl
ether. The yellow band was collected and evaporated in vacuo to give
1,2,3,4-tetraphenylnaphthalene as a yellow oil.
Catalytic experiment: benzoic acid (31 mg, 0.25 mmol), diphenyl-
acetylene (89 mg, 0.5 mmol), Ag2CO3 (138 mg, 0.5 mmol), 1 (2.8 mg,
0.005 mmol) and o-xylene (2 ml) were used.Yield, 12 mg (12%). 1H NMR
(CDCl3) d: 7.63–7.65 (m, 2H), 7.38–7.40 (m, 2H), 7.17–7.32 (m, 10H),
6.82–6.86 (m, 10H) [cf. ref. 1(e)].
Equimolar experiment: benzoic acid (7.5 mg, 0.06 mmol), diphenyl-
acetylene (21 mg, 0.12 mmol), Ag2CO3 (33 mg, 0.12 mmol), 1 (34 mg,
0.06 mmol) and o-xylene (1.5 ml) were used. Yield, 26 mg (98%).
Received: 25th May 2016; Com. 16/4944
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